Telephone switchboard



TELEPHONESWITCHBOARD Filed Dec. 30, 1959 5 Sheets-Sheet 1 k5 E- Q [If-[l "7 E w I I 6 lNl ENTOR I N 7.D.ROBB m I W A T TORNE V March 17, 1942. ROBB 2,276,515

TELEPHONE SWITGHBOARD' Filed Dec. 30, 1939 3 Sheets-Sheet 2 INVENTOR 730. R088 ATTORNEY March 17,1942. RQB'B 2,276,515

TELEPHONE SWITCHBOARD Filed Dec. 30, 1939 3 Sheets-Sheet 3 lNl/ZNTOR 7:0.- ROBB ATTORNEY Patented Mar. 17, 1942 UNTED orrlc Bell Telephone Laboratories,

Incorporated,

New York, N. Y., a corporation of New York Application December 30, 1939, Serial No. 311,738

4. Claims.

This invention relates to telephone systems and more particularly to toll switching systems.

An object of the invention is to provide an improved circuit arrangement for toll switchboards of the type disclosed and claimed in U. S. Patent 1,608,524 to L. F. Porter, whereby more flexible operation is obtained.

A feature of the invention resides in an arrangement of the circuits whereby the operators telephone set is normally conditioned for monitoring, i. e., listening, on the cord circuits, under control of monitoring keys, and can be conditioned for talking and connected to a cord by operation of a talk key only when the associated cord is connected to a line. This permits the operation of the talk key on any cord prior to its connection to a line without sounds affecting the operators transmitter being heard in the receiver.

The invention will be understood from the following description when read in connection with the accompanying drawings, Figs. 1, 2 and 3 of which, when joined as shown in Fig. 4, disclose a complete cord, position, dial and operators telephone circuit.

In describing the operation of the circuit it will be assumed that a call from a coin box station has arrived over a trunk circuit TK (Fig. 1) and is indicated by a line signal (not shown). It will further be assumed that the operator is idle at the moment but has the talk key I00, on cord C, in an operated position in readiness to talk over any line with which she may associate the cord. At this time, it will be noted that relay 200 is operated due to the connection of the operators telephone and that the transmitter is energized in the following circuit, battery, right winding of impedance coil 20I, tip of jack 202 and the operators telephone plug, transmitter T, tip spring of jack 203 and left winding of impedance coil 20I to ground and therefore sounds afiecting the transmitter will cause voltage fluctuations in the primary winding 204 of the induction coil 205 bridged across the circuit. It will be noted, however, that at this time the secondary winding of coil 205 is open at the contacts of relay 200 and hence the voltage fluctuations in coil 205 have no effect on the operators receiver R regardless of the fact that the talk key I is operated which in turn causes the operation of relay IOI to connect the cord into the position circuit where it is open at contacts I02 and I03 of relay I04 and contacts I05 and I06 of relay I01 and therefore disconnected from the operators telephone, When the operator answers the calling trunk by inserting the rear or answering plug I00 in jack I00, ground through an 1,800 ohm resistance (not shown) on the sleeve of the trunk operates sleeve relay I I0 in a circuit which can be traced from ground, sleeve of jack I09 and plug I08, contacts III of operated relay IOI and windings of relays H2 and I I0 to battery. Relay H2 is marginal and does not operate in series with the high resistance of the trunk sleeve.

Relay II 0 in operating operates relay I04 which latter relay disconnects, at its contacts II3, the busy test relay 201 from the tip conductor of the cord, connects the tip and ring conductors of the cord to the telephone circuit over its contacts I03 and I02, closes at its contacts IN, a circuit to operate relay 200 and at contacts II5 connects ground through high resistance M0 to the rear supervisory lamp I I! which lamp, however, does not receive sufficient current through this high resistance circuit to light.

As mentioned above, with the operation of relay IM, the tip and ring conductors of the rear cord, which are connected to the calling trunk, were extended to the operators telephone. circuit, at the right side of Fig. 2, over contacts 03 and I02 of relay I04, contacts H8 and H9 of relay I20 and contacts 208 and 209 of relay 200 and thence through condensers 2I0 and 2 to the outside terminals 'of the secondary winding of induction coil 205, and by the operation of relay 206, the operators receiver R. is connected to a portion of the secondary winding of coil 205. It will therefore be noted that whereas the operators transmitter T was energized as soon as the operators set was plugged into the telephone jacks 20I and 203,'the secondary winding of the coil 205 was not connected to either the cords or operators receiver until a cord was connected to a line on which a talk key was operated.

It will be noted further from the drawings that prior to the operation of relay 200, the operators receiver was connected through the monitoring coil 2I2 to the normally opened contacts of the monitoring key I25, thus enabling the op- Assuming that the line over which the call is to be extended is a ringdown line, the operator will insert the plug I26 in jack I29 whereupon ground through a high resistance (in practice of the order of 1,800 ohms) on the sleeve of jack I29 (not shown), will cause operation of relay I30 in a circuit traced from the sleeve of the jack and plug, contacts I3I of relay IOI, assuming that the talk key I is still operated, and windings of relays I32 and I30 to battery. Relay I32 is marginal and does not operate in this circuit, but relay I30 does operate thereby operating relay I01 to connect the tip and ring conductors of the front cord in parallel with the corresponding conductors of the rear cord which are connected to the calling line and also with the operators telephone set as previously described.

The operator then proceeds to signal the distant operator by actuating front ringing key I21 which causes relays I 28 and I31 to operate in series in a circuitwhich can'be traced from battery, contacts I34 of relay I35, conductor I43, contacts I36 and winding of relay I31,-contacts of key I21 and winding of relay I28 to ground over contacts I38 of relay I39. Relay I31 in operating closes its contacts I40 and opens its contacts I36 thereby closing a local holding circuit for itself and I28. Relay I31 also closes its contacts I4I, and relay I28 closes its contacts I42, thereby completing a circuit to operate relay I35 which, in operating, opens its contacts I34 and removes battery from conductor I 43 thus preventing any other cord relay corresponding to relay I31 from operating as long as key I 21 remains operated. The efiect of this is that the operator can ring on only one cord at a time. Relay I 35 holds operated through its own contact I14 to ground over contacts I4I of relay I 31.

If it is assumed that the talk key I00 is operated on the cord over which we desire to ring, then when relay I31 operated, it closed its contacts I44 thereby completing a circuit to operate relay I45 which can be traced from ground, contacts 243 of relay 206, contacts 244 of relay 200, conductor 245, contacts I15 of relay IOI, upper contacts of the talk key I 00, conductor I46,'contacts I44 of relay I31, contacts I41 of relay I 28 and winding of relay I45 to battery. Relay I45 operates in this circuit and opens its contacts I48 and I49 thereby disconnecting the tip and ring conductors of the front cord from the telephone set and also the corresponding conductors of the rear cord. Relay I45 also closes its contacts I50 thereby locking itself to:

the ground on contact I4I of relay I31.

Relay I28 in operating opens its contacts II thereby disconnecting ground from relay I39 and preventing its operation in case the rear ringing key I52 should be inadvertently operated.

With relays I31, I28 and I35 operated, ringing battery is now connected to the tip of the called line in a circuit which can be traced from 48- volt battery 2I6, resistance 2I1, conductor 2H5} lays I 31 and I 28. Relay I28 releases in normal time but relay I31 releases slowly so that when relay I 28 releases and disconnects the ringing battery 2| 6 from the tip conductor any charge which'may have accumulated on the line due to the ringing current will be discharged to ground through resistance I56 and I51 over contacts I55 and I58 of relay I31 (still operated), contacts I59 and I60 of relay I28 (now released), contacts I6I and I62 of relay I20 and contacts I63 and I64 of relay I35 which relay is held operated at contacts I4I of relay I31. When relay I31 releases and opens its contacts, it releases relay I35, disconnects the cord. from the ringing and coin control equipment in the position, and reconnects the respective tip and ring conductors of the rear and front cords.

The operator may now, or at the end of the conversation, collect or return coins at the calling subscribers station by first operating one or the other of the common coin control keys, CC or CR, and then operate the ringing key associated with the particular cord connected to the line which in the present case is key I52.

If we assume that the operator desire to collect a coin over the trunk line TK, she will first actuate the common coin collect key CC, thereby operating relay 224 in a circuit from battery, winding of relay 224, normal contacts 225 of key CR, contacts 226 of key CC, contacts of 221 of relay 220, conductors 228, and contacts I65 of relay I35 to ground. It will be noted that operation of relay 224 is dependent on the released or non-operated condition of relay I35 and therefore if a ringing key is depressed at the time a coin'controlled key is actuated, the coin control condition will not be established. If the CC key was operated in error, operation of the CR key will release relay 224 and operate relay 220. Operation of relay 224 lights the lamp 229 as an indication that the position circuit is set for coin control, operates relay 230, opens at its contacts 23I the path for operating relay 220, connects positive coin collect potential over its contacts 232 and conductor 233 to the lowermost armature of relay I39, opens its contacts 22I thereby disconnecting the ringing battery 2I6 from conductor 222, thus preventing the subsequent operation of relay I35 from connecting this potential to the line, and by closing its contacts 235, it substitutes a source of tone through transformer 234, on the conductor 222 which tone will be connected to the tip conductor of the cord when relay I35 operates in response to operation of key I 52.

The operator now having the coin collect condition established in the position circuit, and desiring to collect a coin at the substation calling over trunk key TK, operates the ringing key I52 thereby closing a circuit to operate relays I31 and I 39 in a circuit which can be traced from ground, contacts I5I of relay I28, winding of relay I 39, contacts of key I52, winding of relay I31, and contacts I36 thereof, to battery over contacts I34 of relay I 35.

Relay I 31 in operating connects the tip and ring conductors of the rear cord to the inner, upper and lower, armatures of relay I39. Relay I39 in operating opens, at its contacts I38, the operating ground for relay I28 thus preventing this relay from being energized should key I 21 be accidentally operated, and by closing its contacts I66, connects ground to hold relay 224 operated. This holding path can be traced from ground. contacts I66 of relay I39, conductor 236, contacts 231 and winding of relay 224 to battery.

Operation of relays I31 and I39 jointly operate relay I35 in a circuit which can be traced from ground, contacts I4I of relay I31, contacts I61 of relay I39 and Winding of relay I35 to battery. Relay I35 locks to ground at contacts II of relay I31. Relay I35 in operating opens its contacts I34 thereby disconnecting the operating battery for relays I31 and I39, but relay I31 in operating closes its contacts I40, thus providing a substitute battery to hold these two relays operated as long as the contacts of key I52'are closed. Relay I35 in operating also opens its contacts I65 thereby removing ground from keys CC and CR. With relays I 31, I39 and 224 operated, positive coin potential is now connected to the ring conductor of the rear cord in the following circuit: battery, resistance lamp 238, contacts 232 of relay 224, conductor 233, contacts I68 of relay I39, conductor 239, contacts 240 of relay 224, winding of marginal coin pilot relay 24I, conductor 242, contacts I69 of relay I39 and contacts I10 of relay I31 to the ring conductor of the line.

Simultaneously with application of positive coin potentials to the ring conductor, the tone transformer 234 is connected to the tip of the cord as an indication to a service observing operator, that may be listening on the connection, that a coin collect key has been operated. This patent can be traced from tone transformer 234, contacts 235 of relay 224, conductor 222, contacts I53 of relay I35, contacts I1I of relay I39 and contacts I12 of relay I31 to the tip of the cord and thence to the trunk.

If a coin is in the box at the substation, the resistance of the ring conductor to ground will be low enough to permit sufi'icient current to flow to operate the marginal relay 24I which in turn short-circuits the slow-release relay 230 which thereupon releases and lights the coin pilot lamp 213.

When the ringing key I52 is released, relays I31 and I39 release thereby disconnecting coin battery and tone from the ring and tip conductors respectively, releases relay 224, and due to the fact that relay I31 is slow to release, momentarily connects grounded resistances B across the tip and ring to dissipate any charge on the 71 trunk due to the coin potential.

Relay 24! will release when the coin potential is removed from the trunk and the lamp 213 will be extinguished. Release of relay 224 extinguishes lamp 229. leases, the two ends of the cord are connected together again and relay I35 releases which reconnects battery, at its contacts I34, so that operation of another ringing key will be effective. In case either key CC or CR should be operated accidentally, thereby setting up a coin control condition in the position and lighting pilot lamp 229, this condition can be canceled by operatin When relay I31 finally rea.

any ringing key on an idle cord whereupon the circuit goes through its cycle and restores to normal.

The circuit arrangement shown by Fig. 3 provides facility for dialing over either the front or rear cords but as this general arrangement has been in use for some time, and is well known, no further description is deemed necessary.

What is claimed is:

1. In a telephone switchboard, an operators position, lines terminating thereat in jacks, a cord circuit thereat adapted to be connected to said jacks, an operators telephone set comprising a receiver and a transmitter, a monitoring transformer and an operators repeating coil, a monitoring key and a talk key, said receiver being normally connected to one winding of said transformer and the other winding of said transformer being normally adapted to be connected to said cord upon the operation of the monitoring key, said transmitter being connected to the primary Winding of the repeating coil, and means responsive to the joint operation of said talk key and the connection of said cord to a jack to disconnect said receiver from the transformer winding and connect the secondary winding of the repeating coil to the receiver and cord.

2. In a telephone system, an operators position, a plurality of cord circuits thereat, an operators receiver and an operators transmitter, a monitoring transformer having primary'and secondary windings, relay means normally connecting said receiver to the secondary winding of said transformer, a monitoring key individual to each cord circuit adapted when operated to connect the primary winding of said transformer,

over normal contacts of said relay means, to the cord circuit with which the monitoring key is associated, an operators repeating coil also having primary and secondary windings, said primary winding being connected to said transmitter and said secondary winding being adapted to be connected to said cord circuit and said receiver by the operation of said relay means, a talk key individual to each cord circuit, and means jointly responsive to operation of a talk key and the connection of the respective cord to a line to operate said relay means thereby disconnecting said receiver from the secondary winding of the monitoring transformer and the primary winding from the cord and connecting the secondary winding of the repeating coil to the receiver and cord.

3. In a telephone switchboard, an operators position, a cord circuit and lines terminating thereat, an operators telephone set comprising a receiver and transmitter, a talk key, and means jointly responsive to the operation of the talk key and connection of the cord to a line to inductively connect said transmitter to said receiver and cord.

4. In a telephone switchboard, an operators position, lines terminating thereat, a cord circuit thereat adapted to be connected to said line, a monitoring key and a talk key associated with said cord. circuit and arranged to prevent simultaneous operation thereof, an operators receiver, an operators transmitter, a monitoring transformer and an operators set repeating coil each having primary and secondary windings, said transmitter being connected to the primary winding of said repeating coil and said receiver being normally connected to the secondary of said transformer, said monitoring key being adapted when operated to connect the primary winding of said transformer to the cord, and means jointly responsive to operation of said talk key and connection to said cord to a line to transfer said receiver connection from the transformer secondary to'the induction coil secondary and to connect, said induction coil secondary to the cord.

THEODORE D. ROBB. 

